The natural history and management of gastrinomas and other malignant pancreatic endocrine tumors (PET's) in patients without (sporadic disease) or with multiple endocrine neoplasia-type 1 (MEN1) is largely based on antedotal reports and small series. Gastrinomas are the most common symptomatic, malignant PET in patients with or without MEN1 and sufficient numbers of these patients have been entered into our protocols to allow systematic assessment. Studies are now underway, evaluating the natural history of these tumors including the presentation and initial diagnosis, definition of factors determining prognosis and improved methods to diagnose these tumors especially in patients with MEN1. We have recently completed and published our results in 261 patients with sporadic disease [Medicine 79:379-411, 2000; 80:189-222, 2001]. In analyzing the natural history of 57 patients with MEN1 and ZES, we have found almost one-fifth of these patients have an aggressive form of the disease leading to decreased survival. We have identified clinical and laboratory features of this group that can be used to identify them and institute early aggressive treatment. Detailed studies are also underway investigating the management of these tumors including assessment of newer methods to localize tumor extent (endoscopic ultrasound, somatostatin receptor scintigraphy [SRS]), definition of the role of surgical resection in both limited metastatic disease and patients with no hepatic metastases; the role of aggressive resection in selected patients, and the role of surgery in patients with MEN1 or without MEN1. The possible side-effects of longterm acid secretory control are being examined including effects on vitamin B-12 and iron absorption as well as the development of gastric carcinoids. Lastly, medical treatment of advanced disease by chemotherapy, use of interferon, radiation and somatostatin analogues is being examined. This last year the results of our long-term prospective study of the use of octreotide (a long-acting somatostatin analogue) in patients with progressive metastatic gastrinoma has been completed. This study shows octreotide has an effect on tumor growth in 50% of patients with the majority showing a growth stablization. In contrast to the established treatment of chemotherapy with octreotide there are with minimal side-effects and the anti-growth effect was long-lasting showing octreotide should now be the initial treatment of choice for these patients.